(a) Field of the Invention
The present invention relates to an orthogonal frequency division multiplexing wireless local area network (LAN) transmitting/receiving system for providing expanded service coverage, and a method thereof. More particularly, the present invention relates to a method for expanding service coverage of a wireless LAN system.
(b) Description of the Related Art
Recently, in addition to providing an Internet service in an indoor environment, wireless local area network (LAN) techniques have allowed expansion of its service providing area to a small hot spot area, and various applications using the wireless LAN have been rapidly developed.
IEEE 802.11a/b/g are standards for the wireless LAN system. IEEE 802.11b/g are defined in a 2.4 GHz band, and IEEE 802.11a is defined in a 5 GHz band. The maximum transmission speed is 11 Mbps in IEEE 802.11b, and 54 Mbps in IEEE 802.11a/g. Such a wireless LAN system uses an orthogonal frequency division multiplexing (OFDM) method. In addition, a wireless LAN system of IEEE 802.11 n is now standardized.
A configuration of the wireless LAN system according to the IEEE 802.11a standard will now be described with reference to FIG. 1.
Data are transmitted from a media access control layer 11 to a convolutional encoder 15 through a scrambler 13, and the convolutional encoder 15 performs a channel encoding operation. A puncturing unit 17 controls data rates of the data, an interleaver 19 rearranges the data, and a mapping unit 21 maps the data as binary data. A buffering unit 23 stores the binary data, and an inverse fast Fourier transform (IFFT) unit 25 OFDM modulates the data. The data is transmitted to a preamble generator 29 through a multiplex unit 27, and the preamble generator 29 generates a preamble. The modulated data and the generated preamble form an entire frame. The data are modulated by a digital to analog (D/A) converter 31, are amplified to a radio frequency (RF) bandwidth by an RF transmitting unit 33, and are transmitted through an antenna.
A signal received through an antenna and attenuated to a baseband signal by a radio frequency (RF) receiving unit 35 is converted into a digital signal by an analog to digital ((A/D) converter 37. A signal detection and synchronization unit 39 detects and synchronizes time and frequency of the digital signal, and a buffer unit 41 stores the signal. A fast Fourier transform (FFT) unit 43 transforms the signal, a channel estimation unit 45 estimate a channel, and an equalizer 47 equalizes the channel. A demapper 49 converts the signal into binary data and soft-decision data. A deinterleaver 51, a depuncturing unit 53, a Viterbi decoder 55, and a descrambler 57 respectively performs inverse-processes of the transmitter (i.e., deinterleaving, depuncturing, Viterbi decoding, and descrambling processes)
In this case, a configuration of a wireless LAN frame includes a preamble period P10, a signal field period P20, and data field period P30, as shown in FIG. 2.
Here, the preamble period P10 includes a short preamble and a long preamble.
The short preamble is used for performing frame synchronization and coarse frequency synchronization after performing signal detection and automatic gain control.
The long preamble is used for performing fine frequency synchronization and channel estimation of each subcarrier.
A signal field of the signal field period P20 has transmission mode information (i.e., modulation method and code rate information) and frame length information.
Accordingly, the signal field is firstly demodulated to extract the transmission mode and frame length information, and a data field of the data field P30 is demodulated based on the extracted transmission mode and frame length information to obtain receiving data.
Since the demand for wideband for a voice over Internet protocol (VoIP) service using the wireless LAN has increased, studies for increasing a service area (i.e., coverage for the conventional wireless LAN system) have been actively pursued.
However, since the wireless LAN system problematically has narrow service coverage, the service radius in a wireless LAN of IEEE 802.11a/g is approximately 100 m.
In addition, the service coverage is limited since the transmission output is low, and therefore the service radius may be increased when a high gain amplifier and a high gain antenna and sector are used.
However, this may increase the system manufacturing cost, and power consumption in a portable terminal may be increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.